This invention relates generally to vehicle window antennas and, more particularly to a window glass for use in a vehicle such as automobile having both radio antenna elements and defrosting heating elements mounted thereon.
Window glasses of this kind are known and illustrated in FIGS. 9 and 10. The window glass 30 has a defrosting heating conductor 31 mounted on the inner surface of the glass which is exposed to the interior of a vehicle. In addition, the same inner surface has antenna conductors 33 and 35 attached thereto at the top and bottom margins 32 and 24, respectively. Each antenna conductor is connected to a feed pad 38 from which the current generated in the antenna conductor is supplied to a radio receiver (not shown).
Each element 31, 33, 35 may take the form of either a conductive film of transparent material (see FIG. 9) or a printed conductor made from printing and sintering a conductive paste (FIG. 10).
In either case, antenna conductors 33 and 35 are designed and arranged such that they produce a current as large as possible in response to radio waves over the inended reception band of frequencies. To further improve the antenna gain, antenna conductors 33 and 35 are disposed in capacitive-coupling relationship with the heating conductor 31 which, though its primary function is defrosting, is also able to respond to the radio waves.
Unfortunately, to guarantee an antenna gain which is as high as to meet the receiver system, the margin or area reserved for the antenna element should span a length of approximately 150 to 200 millimeters in the vertical direction of the window glass. Therefore, it was difficult for a relatively small vehicle window (e.g. rear-windshield) used in a small-size automobile to mount an antenna thereon that satisfied the required antenna gain or characteristics. In addition, capacitive coupling occurs only between the opposing edges of the heating conductor array and the antenna conductor array, thus limiting the antenna sensitivity.
It is an object of the invention to provide a vehicle window antenna which overcomes the above-mentioned disadvantages.